Over-voltage protecting device



Nov. 8, 1955 Filed Dec. 1, 1951 o. c. BOCKMAN 2,723,367

OVER-VOLTAGE PROTECTING DEVICE 2 Sheets-Sheet 1 Fig/ T' FF'T ven for OZu C71 r5551 a 1 550/01 (2 /1 BY F MQAGW Nov. 8, 1955 o. c. BOCKMAN 2,723,367

OVER-VOLTAGE PROTECTING DEVICE Filed Dec. 1, 1951 2 Sheets-Sheet 2 United States Patent OVER-VOLTAGE PROTECTING DEVICE Oluf Christian Bilckman, Oslo, Norway, assignor to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a Swedish corporation Application December 1, 1951, Serial No. 259,335

Claims priority, application Norway December 4, 1950 4 Claims. (Cl. 31761) The present invention concerns an over-voltage protecting device for high tension networks and has especially for its object to decrease the surge protection level which determines the design of the transformers and apparatus intended to be connected to the network, especially with respect to their insulating parts.

By the lowering of the protection level attained by the invention, it becomes possible either to build the transformers and apparatus more cheaply and thus to make the whole plant cheaper, or, if the machines and apparatus are dimensioned as before, a greater reliability is reached. In both cases the gain attained will be considerably larger than the costs for the protecting device.

Nowadays generally valve type surge diverters are used to protect electric plants against lightning surges. These diverters contain a plurality of ignition gaps and quench gaps or combined quenchand ignition gaps in series with a valve type resistor. When a surge occurs, the spark gaps ignite and a current traverses the valve type resistor to earth. This current will cause a voltage drop in the resistor, which together with the negligible voltage drop over the spark gaps constitutes the residual or discharge voltage. When the surge voltage decreases, the current through the resistor falls down to a value determined by the lower voltage and by the resistance in the resistor which has increased due to the decrease of the impressed voltage. The current through the resistor after the disappearance of the surge is called the follow current of the diverter. The quench gaps are so designed that they areable to interrupt the current at a voltage somewhat higher than the normal voltage. In order that the quench gaps shall be able to interrupt the current, the resistance value of the resistor must not be too low. Generally the quenching ability of the quench gaps will not be above some 50 amperes.

It is apparent that due to above mentioned reasons the resistance value in the surge. diverter must be high enough to limit the follow current to a value that can be interrupted by the spark gaps, and thus the discharge voltage cannot be lowered below a certain limit.

The present invention concerns a device by which the discharge voltage can be made considerably lower than in hitherto known surge diverters, and the invention will therefore allow the use of a lower insulating level, or if the insulating level is retained, the use of a higher transmission voltage. According to the invention the resistance value is chosen considerably lower than hitherto, and further a switching device is inserted in series with the diverter which is arranged to interrupt the follow current through the diverter. In order that there always shall be a surge diverter connected to the network to take care of subsequent surges, the switching device is so designed that it, after the occurence of a surge, before switching out the diverter, introduces a new one between the network and earth. According to the invention the over-voltage protecting device will therefore consist of two or more diverters comprising spark gaps and resistors in series with them, and in series with ICC these diverters a switching device which, actuated by the current through the diverters, disconnects these diverters and at the same time'interrupts the current through them and simultaneously connects in one or more other diverters between the network and earth.

The switching device performing the interruption of:

the current through the diverter or group of diverters, which are ignited, and which also serves to connect in another diverter or group of diverters to the network, shall be as rapidly working as possible in order to avoid an undue heating of the resistances. It is therefore advisable to construct the switching device after the same principle as an air blast circuit breaker, but it must be so designed that it connects in a new diverter or group of diverters before the interruption takes place. If therefore a sub sequent surge occurs immediately after the first one, it will traverse this new diverter or group of diverters which then becomes disconnected after the first diverter again will be connected in between the network and earth, and thus there will always be a diverter or group of diverters ready to take care of occurring surges.

The diverter or group of diverters may either be permanently connected to the line or to earth and the switching device arranged on the opposite side. With respect to the insulation it is most suitable to connect the diverters permanently to the line and to arrange the switching device on the earth side.

It is generally suflicient to use only two diverters which are alternatingly connected in, but it is also within the scope of the invention to replace the single diverters by groups of parallel connected diverters. The invention concerns also a device in which three or more diverters or groups of diverters successively are connected in. In

the latter case the switching device must be designed toperform such a successive switching action and must therefore have a number of switching positions corresponding to the number of diverters or groups of diverters.

On the accompanying drawing Fig. 1 shows an overvoltage protecting device according to the invent-ion, and

Fig. 2 shows indetail the switching device shown in- Fig. 1. Fig. 3 shows schematically a relay controlling the operation of the switching device.

In Fig. l, 1 and 2 designate two known diverters sisting each of two units 1 and 1" and 2 and 2", respectively, which units contain spark gaps and series connected valve type resistors. The diverters are mounted on pillar insulators 3 and 4, which rest on stands Sand 6.

On the top of each of the diverters voltage equalizing umbrellas 7 and 8 are arranged, and the upper ends of the'diverters are by conductors 9 and 10 connected with the line 11, which shall be protected.

Between the diverters there is a switching device 13. This is by means of the insulators 16 and 17 carried by a stand 18. 14 designates a box containing outlet and operating valves and electricallycontrolled pilot valves for said outlet valves. 15 is a box containing a current transformer and a relay changing from one position to the other, each time it is traversed by a current and then alternatingly closing the current through the electrical control valves of the switching device 13. 19 is a pipe line for the delivery of compressed air to the switching device 13. 20 and 2.0 designate conductors connecting the earth side of the diverters 1 and 2 with the switching device 13.

The switching device shown in Fig. 2 consists of a longitudinally extending cylinder 21, which in each end is provided with bushings 22 and 23. The inner ends of these insulators carry sleeve contacts 24 and 25 and arcing contacts 26 and 27. In the cylinder 21 there is a further cylinder 28, in which a piston 29 slides, on which piston the movable contacts 30 and 31 are afiixed. The cylinder 28 is attached to the cylinder 21 by means of con 3 the two pipes 32 and 33. The two contacts 30 and 31 are pipe formed and attached to the piston 29 so that the bores in the contacts coincides with the holes 34 and 35 in the piston.

Compressed air is delivered to the container 21 from pipe line 19 over pipe line 46. From the pipe line 19 compressed air is further delivered to the operating cylinders 38 and 39 over the valves 40 and 41 controlled by the current through the coils 42 and 43. The pistons in theoperating cylinders 38 and 39, respectively, actuate the valve members in the outlet valves 36, 37, respectively.

If for instance in the position shown on the figure the coil 43 is traversed by a current, the valve 41 will be opened and gives access for compressed air to the cylinder 39, so that the piston in it will move upwards and open the outlet valve 37. The compressed air in the cylinder 21 will then move the piston 29 to the right until the contact 31 engages into the contact 25 and the contacts 24 and 30 are separated.

1n Fig. 3 47 designates the primary winding of a current transformer 47, one end of which is connected to earth and the other end of which is connected by means of the conductor 49 to the control box 14 of the switching device 13. The current transformer is suitably together with a current relay 50 enclosed in the box 15 attached on the stand 18. The current relay 50 consists of two iron cores 51 and 52, and between them there is an armature 53. The two cores are magnetised by two windings 55 and 56, which over contacts 57 and 58 alternatingly are connected to the secondary winding 47". The control coils 42, 43 are over the contacts 59 and 60 connected to the D. C. source 61. In series with the D. C. source 61 there is a contact 62 operated by a coil 63 fed from the winding 47". The contact 62 is normally held in open position by spring 64 but is closed by the current traversing transformer winding 47". In order to delay the opening of contact 62, this is connected with a dash pot 65. After a surge, the follow current flowing through the diverter 1 over contacts 24 and 30 and through the primary winding 47 in the box 15 and to earth will cause a current through the secondary winding 47" of the transformer over the contact 58, through the winding 55, and the field then generated in this core 51 is sufiiciently strong to pull the armature 53 away from the permanent magnet 52. The contact 60 is then opened and contact 59 becomes closed, so that the coil 43 is connected to the D. C. source 61. The compressed air on the left hand side of the piston 29 will then move the piston 29 to the right until contact 31 engages contact 25, and at a further motion of piston 29 the contacts 24 and 30 are separated. The compressed air in cylinder 21 will enter contact 30 and then extinguish the are between contacts 24 and 30. At a subsequent current impulse the above described procedure is repeated, but now the armature in the relay is moved in opposite direction, so that instead the coil 42 is connected in and the piston 29 moved back to the position shown in Fig. 2.

The switching device shown in Fig. 2 is only shown as an example and can be replaced by any other sufficiently rapidly acting device, for instance some mechanical or electronic coupling device, and the relay shown in Fig. 3 is only to be regarded as an example of a release device.

I claim as my invention:

1. An over-voltage protecting device for a high tension electrical network, comprising a series arrangement of a plurality of surge diverters each including a spark gap and a valve-type resistor in series relation and a current responsive multistage switching means of the make-beforebreak type, wherein each of the said surge diverters is at one end permanently connected to a stage terminal of the said switching means, means being provided for connecting one end of the said series arrangement permanently to the network to be protected and the other end permanently to earth.

2. A device according to claim 1, comprising at least three surge diverters, the switching means being provided with movable contact means covering at least two adjacently positioned stage terminals.

3. A device according to claim 1, wherein the switching means is provided with follow-on current interrupting contacts.

4. A device according to claim 1, in which the said switching means comprises in combination a compressed air container, a pair of insulator bushings extending through the wall of the said container, a stationary electrical contact mounted at the end of each of the said insulators and located inside the said container, a stationary comperssed air cylinder inside the said container, a reciprocally movable piston situated in the said cylinder, a pair of tubular electrical contacts carried on opposite sides of the said piston and extending through the walls of the said cylinder and each adapted to cooperate with one of the stationary contacts, a pair of inlet control valves associated with the said cylinder, and actuating means for each of the said control valves including a current responsive device connected through the said surge diverters to the electrical network to be protected.

References Cited in the file of this patent UNITED STATES PATENTS 306,697 OSullivan et al. Oct. 14, 1884 455,955 Van Nuis et al. July 14, 1891 860,157 Shirk July 16, 1907 1,651,872 Creighton Dec. 6, 1927 2,006,179 Price et al. June 25, 1935 2,079,723 Swart May 11, 1937 2,224,749 Slepian Dec. 10, 1940 FOREIGN PATENTS 207,769 Germany Mar. 2, 1909 

